REPORT ON THE PTEROPODA. 
61 
marginal teeth, and, according to Sars, 1 its formula is 2-1-2 ; whilst 
in Nautilus, according to Kefersteiu, 2 there are two marginal teeth on 
each side, so that the radular formula is 2-2-1-2-2. 
In the Pteropoda, on the other hand, the radula varies within wide 
limits (the extreme formulae being 1-1-1 and 17-1-17), and besides 
is characterised by the uniformity of all the lateral teeth, which differ 
only in their respective dimensions, their form not distinguishing, among 
them, so-called marginal teeth. 
c. Mandibles. — In all the Cephalopoda these are dorsal and ventral; in the 
Pteropoda, on the other hand, they are lateral, sometimes situated 
ventrally side by side (Gymnosomata). 
d. Salivary Glands. — In the Cephalopoda there are generally two pairs of 
these, which consist of two distinct portions, viz., the distended glandular 
mass and the narrow excretory duct. In the Pteropoda there is never 
more than one pair of salivary glands, which vary in length and do not 
exhibit any distinction between duct and gland. 
e. (Esophagus. — A crop is present in the Cephalopoda but not in the Pteropoda. 
f. Stomach . — This organ in the Cephalopoda never possesses any masticatory 
plates, even in the embryonic condition ; on the contrary, the Theco- 
somatous Pteropoda have them always, and according to Krohn 3 the 
Gymnosomata have them during their larval development. The 
Cephalopoda have a gastric caecum into which the ducts of the liver 
open ; upon these latter is situated the gland commonly known as a 
“ pancreas.” The Pteropoda have neither such a caecum nor “ pancreas.” 
g. Intestine. -—In the Cephalopoda this organ terminates in the middle line, 
whilst in the coiled Thecosomata (Limacinidae) and in the Gymnosomata 
it ends on the right side (in the Gymnosomata it appears to be ventral 
in consequence of the reduction of the pedal face ; in reality it would be 
quite lateral if this last were of larger size) ; in the straight Thecosomata 
(Cavoliniidae and Cymbuliidae) it terminates on the left side, in conse- 
quence of the rotation which was explained at the end of the first part 
of this anatomical Report. 
B. If we consider the organs of circulation, respiration, and excretion, we see that in 
the Pteropoda the heart is asymmetrical, as is also the gill when it exists, whilst in the 
Cephalopoda these organs (heart and gills) are quite symmetrical. In the same manner 
1 Mollusca regionis arcticse Norvegiae, pi. xvii. fig. 2; see also Steenstrup, Oversigt k. Danslc. Vid. SelsJc. 1< err - 
handl., 1880, p. 10. 
2 Die Klassen und Ordnungen des Thierreichs, Bd. iii. pi. cxv. figs. 2, 3. 
3 Beitrage zur Entwickelungsgeschichte der Pteropoden und Heteropoden, pp. 6, 14. 
